Shaped rubber articles comprising, for example, ethylene-propylene copolymers, ethylene-propylene-diene terpolymers or styrene-butadiene copolymers are frequently used for the preparation of gaskets and automotive weatherstrip seals. The elastomers are typically attached to the respective surface like, for example, an automobile frame by means of a pressure-sensitive adhesive film which provides easy handling and performance advantages such as excellent sealing and low weight compared to other systems like liquid adhesives or mechanical attachment.
Rubbers are low surface energy materials having various degrees of elasticity which do not bond effectively to adhesives in general and, in particular, to pressure-sensitive adhesives. Different methods have been proposed so far to provide a durable bond between rubber materials and the pressure-sensitive adhesive.
EP 0 384 598 describes a dual-functional adhesive tape comprising a polyolefin heat-activatable adhesive layer having a graft-polymerized monomer coating, a pressure-sensitive adhesive layer, and a release liner. The heat-activatable adhesive layer comprising the heat-activatable layer, the primer layer, the pressure-sensitive adhesive layer, and the release liner is heat-laminated to a shaped rubber article by using specifically designed equipment. Then the liner is removed from the pressure-sensitive adhesive layer and the resulting composite structure is pressure-bonded to the respective surface.
JP 07 100 901 discloses a double-sided tape comprising a hot-melt adhesive layer, followed by a relatively thick layer of an acrylic foam, a pressure-sensitive adhesive layer and a liner. The double-sided tape is heat-laminated to a vulcanized rubber substrate such as EPDM (ethylene-propylene-diene terpolymer) directly after vulcanization extrusion while the rubber is still hot. WO 95/13184 describes a similar double-sided tape which is heat-laminated, for example, onto an EPDM profile.
The processes described in EP 0 384 598, JP 07 100 901, and WO 95/13184 do not fulfill all practical requirements to a desirable extent because they do not independently allow independent selection of the adhesive layer.
The temperature window for heat-laminating the double-sided tape to the shaped rubber article is rather narrow because a lamination temperature of at least 100.degree. C. is required on the one hand to provide an acceptable bonding to the rubber article, while on the other hand, the temperature for the heat-lamination step must not be chosen too high in order to avoid an irreversible deformation and/or decomposition, in particular, of the release liner. The narrow temperature range accessible is disadvantageous from a processing point of view. This is especially true if the tape is laminated to the rubber article, and then the rubber article is heated to cure or vulcanize the rubber.
Furthermore, shrinkage of the polyolefin-based elastomer and/or the hot-melt adhesive is often observed on cooling which can cause the pressure-sensitive adhesive layer to wrinkle which results in poor adhesion between the pressure-sensitive adhesive layer and the surface it is applied to.
Therefore, one object of the present invention is to provide a process to render substrates comprising a shaped rubber article, receptive to the application of a pressure-sensitive adhesive layer. Other objects of the present invention can be taken from the following detailed description of the invention.